Organic Light Emitting Diode (OLED) display is one of the hot spots in the current research field. As oxide Thin Film Transistors (TFTs) have higher mobility, more stable characteristics and better process uniformity, they are used in OLED display apparatuses to form pixel unit circuits.
However, when a negative bias voltage is applied to an oxide TFT, the larger a negative bias voltage of a gate-source voltage (Vgs), the more a negative shift of a threshold voltage (Vth). Therefore, it results in electric leakage in the oxide TFT acting as a switch in a light emitting phase, thereby causing a display panel not to display normally.